You have to realize that the top left hanjie is perfectly left-right symmetrical, and (other than that one missing dot) up-down symmetrical, and symmetrical across the diagonals too. There's only one possible placement of the last 8 dots that satisfies that.
Two ways to solve the "Winter" season (top left corner) but other than that it was completely logical. The last 8 or so squares are fairly easy to figure out once the rest of the puzzle is completed. Thanks for the fun! ~:)